Enclosures for electrical equipment typically require ventilation to allow the equipment to expel waste heat to an external environment to avoid overheating. In applications where electrical equipment is to be used in remote locations, for example in mobile radio telecommunications base stations, equipment is typically left unattended for extended periods. To ensure that the temperature of the equipment is kept within a preferred temperature range, additional cooling and ventilation apparatus is normally required. Depending on complexity, this cooling equipment consumes energy, which is both expensive and sometimes in limited supply, and also require maintenance to avoid the costly implications of failure.
In a typical radio telecommunications base station, electrical equipment operating the radio frequency (RF) signals is kept inside a ventilated cabinet, which itself is kept within a sealed equipment room providing protection from external conditions. Often, fans within the cabinet circulate air through the electrical equipment to provide cooling, and the air temperature within the equipment room is maintained through the use of an air conditioning unit, which expels waste heat generated by the electrical equipment to the external environment. The air conditioning unit must work to maintain the temperature of the interior of the room within a desired range, to ensure that the equipment within the room operates reliably. This uses a significant amount of power in addition to that required to operate the electrical equipment itself.
A backup power supply in the form of a cabinet of batteries (typically lead-acid batteries) is often necessary in case of a break in electrical power to the equipment room. Such batteries also need to be kept within a desired temperature range, this range being generally more stringent than for other electrical equipment. In a typical equipment room therefore, the air conditioning unit often operates to maintain an internal temperature range dependent upon the requirements of the batteries rather than of the electrical equipment, which is generally able to operate at higher temperatures without any problems. This results in the air conditioning unit having to work harder than is strictly necessary to maintain proper operation of all equipment in the room.
In temperate climates such as in the UK, the ratio of cooling power to equipment power is approximately 1 to 4. So if 4 kW is used by the electronics 1 kW will typically be required by the cooling system. In hotter climates this ratio may reduce to 1 to 3 or even 1 to 2. Clearly in summer the actual day to day consumption may be much higher, but these loads may be offset to some extent in winter.
Therefore an air conditioning unit in a typical equipment room may operate at up to 1 kW, compared with the operating power of the other electrical equipment of up to 4 kW. This requirement can be reduced by providing for separate cooling of the battery backup, allowing the internal temperature of the room to rise to a higher maximum temperature. For example, ensuring the whole room is kept at a temperature of below 20° C. to accommodate battery requirements will tend to use substantially more power than allowing the maximum temperature to rise to 35° C., at which temperature most electrical equipment will still operate without problems. This does not, however, remove the need for air conditioning of such rooms, as some cooling will still be required to prevent the maximum temperature from being exceeded under certain conditions.
A further problem with using air conditioning units in equipment rooms, particularly when such rooms are in remote locations, is that of servicing and repairing. If an air conditioning unit breaks down in use, the electrical equipment is put at risk of failure, and a specialist engineer (usually different from an electrical equipment engineer) must be called out to fix the unit. This can substantially add to the cost of maintaining such equipment rooms. It might also not be known, for example when an equipment room provides an automatic failure indication, what has caused the failure. An electrical equipment engineer could therefore be called out, when what is required is an air conditioning engineer. Multiple visits can then further add to the costs of maintaining operation.
One common alternative approach is, instead of keeping the equipment room sealed and refrigerated, to maintain a high air flow through the room by means of a large fan arranged to force air through air vents provided in the room. To maintain a desired temperature range, however, and to minimise a temperature differential between the interior and exterior of the room, a large airflow is required, requiring a large and powerful fan. Furthermore, air being drawn through the room will tend to draw dirt and dust from the external environment into the room, so the airflow will need to be filtered. Adding filters will inevitably result in a requirement for maintenance visits to check and replace the filters so that a sufficiently high airflow can be maintained. Simply replacing air conditioning with fan cooling does not therefore fully address the problem of requiring separate maintenance visits, nor does it necessarily substantially reduce the power requirements of the room, since large fans require large power inputs. High airflows also tend to draw in more dirt and dust, causing filters to eventually clog.
An improved alternative to the use of air conditioning or large fans is to direct heat generated by the electrical equipment within the room to the external environment, for example by using exhaust ducts extending from the equipment cabinets to the outside wall of the room. Air drawn into the equipment cabinet by an internal fan can then be exhausted to the external environment more directly, reducing heating of the room by heat generated by the electrical equipment. This results in a much reduced need for airflow through the room. Smaller fans, with much reduced power requirements, can then be used to extract air from the room, replacing the air through intake vents in the room.
The above solution does not, however, remove the need for maintenance visits, because air filters will still be required in the intake vents in the room, and these will occasionally need to be replaced.
It is an object of the invention to address one or more of the above mentioned problems.